The result hands a mighty mandate to the veteran left-winger to pursue his vision for the party.

For years, people on the left have imagined what would happen if Labour was led by someone who truly shared their values, who had not compromised his or her principles, and who did not look and sound like the sharp-suited politicos who run around Westminster.

But will he drive the party of Tony Blair and Gordon Brown off a cliff? If he survives to lead Labour into the 2020 election, will the campaign be a kamikaze mission?

There are good reasons for thinking that Mr Corbyn will surprise pundits who think he is about to send Labour crashing into oblivion in a righteous fireball.

This is a man who understands how to win elections.

He first won Islington North with a majority of 5,607 in 1983. In May he won it again but with a majority of 21,194 votes, securing an extraordinary 60.2% of the vote.

His 59.5% victory in the leadership election is yet more proof of his skills as a communicator, campaigner and strategist.

In this contest he was up against Andy Burnham – a former Health Secretary, Culture Secretary and Chief Secretary to the Treasury – and Yvette Cooper, whose past high-profile roles include Work and Pensions Secretary. He also faced energetic competition from Liz Kendall, seen by some as the keeper of the Blairite flame.

Jeremy Corbyn was expected to win - but the scale of his victory in all sections of the Labour electorate is spectacular (Image: Stefan Rousseau/PA Wire)

This trio of rivals had impeccable contacts, huge experience and a wealth of endorsements. In contrast, he had secured the bare minimum of nominations and had never held a frontbench post.

But he outmanoeuvred them all and staged one of the biggest upsets in modern political history.

Not only did he secure the backing of important trade unions, he won the support of thousands of people who signed specifically up to vote for him. Of the 105,598 registered supporters who took part in the election, 88,449 voted for Mr Corbyn.

Despite the committed efforts of their teams, they completely failed to connect with legions of potential supporters. Mr Corbyn did.

There is a world of difference between recruiting the support of tens of thousands of idealists and making serious inroads with the seven out of 10 people who did not vote Labour at the recent election – but Mr Corbyn is canny enough to recognise this.

He will want to map out a strategy that can put Labour on a path back to power. He will not want to go down in history as the man who killed the party of Attlee and Bevan.

Mr Corbyn could have walked out on Labour over the introduction of tuition fees or the invasion of Iraq. He could have been a giant cheese in one of the many parties on Britain’s radical left but he has stuck with the party.

He will want his tenure to be a time for restoration and renewal, not disintegration. And he will have by his side one of the canniest campaigners in modern politics.

Tom and Jerry: Tom Watson and Jeremy Corbyn are entrusted with the future of Labour (Image: Stefan Rousseau/PA Wire)

Newly elected deputy leader Tom Watson was a super-insider throughout the Blair/Brown era and campaigns forcefully on subjects close to his heart. He has a pivotal role to play in both keeping the party together and turning the thousands of people who voted for Mr Corbyn into committed activists.

Within moments of the result being announced at the QEII conference centre, Mr Corbyn made it clear he wants Labour to survive as a big tent party. The warmth of his praise in his acceptance speech for the other candidates – in particular Ms Kendall – signals that he has no interest in purging Labour less radical figures.

He would be much more vulnerable to coup attempts if he had won on the back of second preference votes or performed badly with full party members.

But of the 245,520 members who voted, he won the support of 121,751. Despite being a household name in Labour circles, Mr Burnham could only muster 55,698 and Ms Cooper 54,470, with Ms Kendall netting 13,601.

Andy Burnham and Yvette Cooper were out-campaigned by Jeremy Corbyn

Those who long for Labour to focus on winning back the Labour-Tory marginals in England that will decide the outcome of the next election may be appalled their party has turned its back on the electoral lessons of the Blair era. They may regard the election of Mr Corbyn as a spectacular act of self-indulgence which will make it more likely the Conservatives will enjoy at least a full decade of majority Government with profound consequences for the country.

Nevertheless, Mr Corbyn is the undisputed winner and rejecting his leadership would involve rejecting the will of the Labour electorate.

In the United States the race is on for the Democratic presidential nomination and 74-year-old Vermont senator Bernie Sanders, a gleeful socialist, has stunned the party establishment and alarmed Hillary Clinton’s supporters with the success of his campaign so far.